Potential of Bacillus aryabhattai to Promote Plant Growth and Mitigate the Effects of Water Deficit

The functional roles of endophytic Bacillus and Pseudomonas bacteria to improve tomato and bean plants’ growth under induced-drought stress conditions

Drought is a major constraint to crop productivity, highlighting the need for sustainable approaches to improve plant resilience. In this study, three endophytic bacteria, Bacillus subtilis BS-114 and BS-116, and Pseudomonas wadenswilerensis PPW-26, previously selected based on their plant growth-promoting traits and genomic potential, were evaluated for their ability to enhance drought resilience in common bean and tomato. Their effects were investigated through in vitro screening under polyethylene glycol (PEG)-induced drought, greenhouse drought validation, and open-field evaluation. Bacterial inoculation improved seed germination, seedling vigor, and plant water status under PEG-induced stress, with strain-dependent responses observed between crops, with the most pronounced effects observed in bean. Under greenhouse drought, inoculated bean plants exhibited improved photosynthetic performance and relative water content, together with reduced oxidative damage and proline accumulation, suggesting enhanced physiological adjustment to water deficit. These responses were associated with changes in the expression of drought-responsive genes involved in abscisic acid signaling, antioxidant defense, and osmoprotection, and were accompanied by a 52% increase in yield compared with non-inoculated drought-stressed plants. Based on greenhouse performance, a consortium containing BS-114 and two additional Bacillus strains was further evaluated under field conditions, where crop productivity was comparable to conventional NPK fertilization and a commercial algae-based biostimulant. Overall, these findings highlight the potential of beneficial endophytic bacteria isolated from medicinal plants to improve drought resilience, accompanied by changes in plant water status, hormonal signaling, and oxidative stress responses.

Bacillus Aryabhattai Mitigates Water Stress in Wheat by Enhancing Vegetative Development, Dry Matter Accumulation, and Yield

Bioactivity of Ascophyllum nodosum in Mitigating Water Stress Induced by PEG-6000 in Maize Seeds

Water deficit is one of the main limiting factors for crop establishment and productivity, particularly during seed germination and early seedling development. This study aimed to evaluate the biostimulant potential of Ascophyllum nodosum extract applied to maize (Zea mays L.) seeds subjected to osmotic stress induced by polyethylene glycol (PEG-6000). Three independent bioassays were conducted under controlled conditions. In the first assay, osmotic potentials ranging from 0 to −0.8 MPa were evaluated to characterize stress levels and identify conditions representative of moderate and severe water deficit. In the second assay, increasing doses (0 to 2.0 mL kg−1 of seeds) of a commercial A. nodosum-based extract and its isolated mineral fraction were evaluated to determine the optimal application range. In the third assay, the selected treatment was evaluated under control conditions and under moderate (−0.6 MPa) and severe (−0.8 MPa) osmotic stress. Germination percentage, normal and abnormal seedlings, radicle and epicotyl length, and seedling vigor index were assessed. Osmotic stress progressively reduced germination and seedling growth, with the strongest effects observed at −0.6 and −0.8 MPa. Seed treatment with A. nodosum extract did not impair final germination but improved seedling development in a dose-dependent manner. The highest efficiency was observed at intermediate doses, with maximum normal seedling percentage predicted at 0.45 mL kg−1 and maximum radicle growth at approximately 0.66 mL kg−1. Under water deficit conditions, the complete extract promoted greater improvements in seedling performance than the mineral fraction, indicating that the beneficial effects were mainly associated with bioactive organic compounds rather than mineral nutrition alone. These findings provide new evidence that dose optimization is essential for maximizing the efficiency of seaweed-based biostimulants and demonstrate the potential of A. nodosum seed treatment as a sustainable strategy to improve maize establishment under water-limited conditions.

Chemical treatment and inoculation with beneficial bacteria in maize seed germination

Maize (Zea mays L.) is one of the most widely cultivated cereals globally and the second most produced grain in Brazil. To increase crop grain yield, the application of plant growth-promoting bacteria (PGPB) as inoculants has gained prominence. This study evaluated the effects of inoculation with Azospirillum brasilense, Bacillus subtilis, Bacillus amyloliquefaciens, and Priestia aryabhattai, with and without chemical seed treatment, on maize seed germination and early seedling development. The experiment was conducted in two settings: laboratory (germination test using Germitest paper) and greenhouse (sand bed). A completely randomized design (CRD) was used, arranged in a 2 × 5 factorial scheme (with and without chemical treatment × five inoculants), with four replications. Results indicated that A. brasilense showed the best performance across both environments, promoting higher germination rates, root length, and root dry mass, especially in seeds without chemical treatment. P. aryabhattai also showed positive effects, though to a lesser extent. In contrast, B. amyloliquefaciens negatively impacted germination, with a higher percentage of dead seeds and lower seedling vigor. Chemical seed treatment with fungicides and insecticides negatively influenced some growth parameters and reduced the effectiveness of certain inoculants, likely by affecting bacterial viability. A significant interaction was observed between inoculant type and seed treatment for root dry mass. It is concluded that inoculation with A. brasilense, particularly in untreated seeds, is a promising strategy to enhance maize seed germination and early growth, highlighting its potential as a sustainable alternative to improve crop establishment and initial development.

Morphophysiological responses of soybean seedling to bioinputs based on Bacillus spp.

Abstract The high demand for soybeans in Brazil requires seeds with high physiological quality, enabling the establishment of vigorous seedlings. Abiotic stresses can limit seedling development. In this context, bio-inputs based on Bacillus spp. have stood out, acting in the promotion of root growth, nutrient availability, and induction of resistance. Thus, the objective was to evaluate the action of a commercial bio-input based on Bacillus spp. bacteria on the physiology of soybean seedlings. The bio-input was inoculated in sand substrate in trays, at concentrations of 0 (distilled water); 50; 100; 150 and 200 µL. Two hundred seeds were sown per treatment, with 4 repetitions. The emergence of soybean seedlings, length and dry mass, as well as gas exchange, chlorophyll a fluorescence, and anatomical and histochemical analysis of the leaves were analyzed. Doses between 100 and 150 µL were able to improve seedling performance, length, and biomass. All doses of the bio-input provided ideal values of potential quantum yield of PSII (Fv/Fm), close to 0.83, reaching a maximum at the estimated dose of 132.07 µL, with a peak of 0.77. The leaves of seedlings treated with the bio-input showed greater xylidine staining, indicating an increase in protein compounds and, consequently, expansion of intercellular spaces in the spongy parenchyma, in contrast to the control group, which showed less xylidine staining. Furthermore, a strong positive correlation was found between the potential quantum yield of PSII (Fv/Fm) and growth variables, including emergence (EM), shoot length (CA), root length (CR), shoot dry mass (MA), and root dry mass (MR). The bio-input was able to stimulate the initial growth of soybean seedlings, mainly at concentrations of 100 to 150 µL, although further studies are needed to validate its action under real cultivation conditions.

Growth and Physiological Responses of Petunia to Chitosan and Arbuscular Mycorrhizal Fungi Under Sustained Water Content Reduction

Reducing irrigation inputs is essential for sustainable container crop production; however, the ability of biostimulants to mitigate the effects of deficit irrigation on ornamental crop quality and postharvest often may be crop-specific, product-specific, and application-specific. Two independent experiments were conducted to evaluate whether chitosan applied as a substrate amendment or arbuscular mycorrhizal fungi (AMF) applied during germination could improve growth, physiology, and postharvest performance of petunia ( Petunia milliflora ‘Picobella TM Pink’) under sustained water content reduction. Plants were grown under three container capacity (CC) treatments (100%, 70%, and 40%) combined with chitosan application timing (no application, week 1, or week 3) or AMF application (with or without). After production, plants were exposed to postharvest environments at 30 °C or 40 °C for 2 weeks. The growth index and canopy area decreased by 10% to 40% relative to plants grown at 100% CC under 70% and 40% CC; however, flower coverage percentage remained unaffected during production. Water use reduced by 20% at 70% CC and by up to 50% at 40% CC, while irrigation water use efficiency (IWUE) was maintained with all CC treatments. In the AMF experiment, plants grown at 40% CC with AMF exhibited the highest IWUE and increased root colonization under severe deficit irrigation. Photosynthetic pigment concentrations were generally maintained under deficit irrigation, whereas malondialdehyde concentrations temporarily increased at week 4 under 40% CC, indicating increased oxidative stress. Neither chitosan nor AMF consistently enhanced plant growth or reduced biochemical stress indicators under the evaluated conditions. Chitosan application timing strongly influenced plant responses, with week 3 applications reducing growth and increasing oxidative stress across CC treatments. During the postharvest evaluation, temperature was the primary factor affecting plant performance, with plants maintained at 40 °C exhibiting lower flower coverage and canopy area compared with plants maintained at 30 °C. The combination of deficit irrigation and chitosan application showed limited potential to improve postharvest heat tolerance, whereas AMF application did not improve postharvest performance. Overall, petunia demonstrated substantial tolerance to sustained deficit irrigation, and 70% CC appeared to be a practical strategy for reducing irrigation inputs while maintaining marketable crop quality.